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Wonder if I could have some help. I bought an XJS V12 convertible a couple of years ago and have been slowly restoring it, its now done nearly 46k miles. Amongst other things had all the bodywork done, rear quarters, sills, front arches, lower front cross beam etc, shes starting to look good....
I am a big Jag fan and had around 9 over the years and my daily is an XJ Supersport so thought I would buy an older one!
On a mechanical front rear axle has been stripped and rebuilt, new brakes front and rear, oil cooler replaced and various engine leaks fixed. It has never really run right and always felt a bit lacking in smoothness considering its a big V12. I took the car home (it was stored at work) and realised the garage that did the work did a poor job and it was still leaking from the rocker covers and was generally a bit sorry for itself in the engine bay area so thought I would strip it down and get it running perfectly.......
Since I have done the work it won't run at all! It turns over, fires very lumpy, chugs, sounds like its running on 3 or 4 cylinders and then dies. It does this consistently whatever I do. As a run down since the car last ran I have done the following:
Cleaned distributor and rotor arm (this was new 3 years and 2000 miles ago)
New spark plugs, Denso and gapped correctly
New ignition leads
New fuel injection wiring harness
Stripped and rebuilt fuel injectors, newlines, pintels etc
New rocker cover gaskets
Throttle blades reset as per factory
New extra air valve
New water temp sensors
The things I have checked and had no effect on the symptoms:
Put the old plug leads back on
Checked for spark on each plug lead
Measured fuel pressure at fuel rail
Grounded out water temp sensor
Plenty of fuel
Put small clear bags on each injector to check each injector fires
I am an automotive engineer so like to think I have gone through the logical steps, although working on this engine has been an eye opener, seems super simple and tough yet complex and fickle at the same time!
Any thoughts from the V12 seasoned people on here?!
New fuel?
Have you checked the swirl pot below the fuel tank to see if it is full of crud?
Same with the fuel filter.
Crank shaft position sensors? There are 2 I believe.
Much more to check yet!
Looks nice though.
One of the Vital Components that is often overlooked is the 'Resistor Pack' aka the 'Silver Box' with the Plug and Socket, which is down by the Headlamp Nacelle (drivers side on a UK Car) as its is a bit of a PIA to get to
But if the Plug and Socket is dirty, then it can play Havoc with the Firing of the Injectors and was one of the reasons that my Car 'Cherry Blossom' was running like a Tractor, when She eventually Started
Although the Primary reason for this was that I had inadvertently connected the Two Coils to the Wrong Bank of Cylinders on my Marelli Car
The Lower Coil the Red one goes to 'A' Bank
The Upper Coil the Yellow one goes to 'B' Bank
And I had these the wrong way round
Other possibilities:
(1) Blocked Fuel Filter which could give the Correct Fuel Pressure when Tested but could be intermittent when actually running
(2) Fuel Pump on the way out
(3) Any droplets of Water anywhere near the engine
You can read about the 'Saga' of how I got her Started not from a 'Breakdown Service' or by reading a Manual but with loads of invaluable help from 'Greg' in France and 'Grant' 'The Wizard of Oz' in errr.. Australia
What either of these 'Guys don't know you don't need to know'
Getting 'Cherry Blossom' Started when She wouldn't go
We tried every trick in the book and one of them Worked!
Personal preference, Throw those damn "Denso" Plugs in the Trash!!!
They earned me one heck of an azz chewing many years ago. I was the mechanic for a Kawasaki Dealer, in the late seventies. I had just finished a 600 mile tuneup on a KZ 400, a simple 2 cylinder. The owner had requested Nippon Denso plugs. He picked the bike up just before I went to lunch. Upon returning from lunch I saw the "Bike" was back in the work area. I asked my Boss why? He proceeded to chew my azz, and tell me, the guy was pissed, and would never buy another GD thing from us as long as he lived! I asked what the problem was, and he said it wouldn't hardly run? I popped the point cover off, and checked the gap OK? started the bike and sure enough it ran like dog ****. I checked the air intake, and everything else, and found no failure???? I told my Boss give me a set of NGK plugs, as this wasn't the first time I'd had Denso plugs fail. Sure enough, I gapped and installed the NGK's and all was cured. The Bike ran perfect. I told the boss I'll never install another Denso Plug in anything. If a customer wants them, they will have to install them themselves!
I don't know if that will fix your problem or not. But I damn sure wouldn't have spent my money on them. Just my Thoughts.
Just to clarify,car is a 1988 and has the Marelli ignition system. I have focused my fault diagnosis on to things i have changed or fiddled with as I drove it into the garage.
Couple of questions again...
has anyone else ran Denso plugs and they have been fine?
Where is the fuel filter located,presumably under the back of the car by the pump?
There is a smell of fuel around the back of the car, I have read this is normal.....doesn't seem normal to me, can anyone confirm or deny this?
Appreciate fuel pressure at the fuel rail is ok but also know this does not necessarily represent flow rate,if I put a pie from the fuel rail entry into a bottle what l/h can I expect from a good pump?
No water anywhere near the engine
I have not checked the resistor pack, the bonnet of off the car so I locating it should be easy bit how to I then check its function?
I had a connector fail on the crank sensor before but it didn't even attempt to fire, at the moment it seems to want to go, chugs a bit and then dies.
Orangeblossom - I have made myself a coffee and shall read your thread!
Thanks again
Simon
Last edited by Skinthespin; 12-29-2018 at 03:22 AM.
The dizzy turns anti-clockwise, the leads just might be fitted assuming clockwise
Check that plug A1 (RHS front cylinder) is sparking just before piston A1 comes up to compression stroke TDC; do the same for B1 (front LHS).
The marelli has a two level dizzy and rotor, and two king leads (I think). The marelli experts can tell you what goes where, so ask them for a pic/the correct way to connect them.
Pull an injector on a front cylinder, as they are easier to remove, and do a spray test.
There are two ignition amplifiers on the panel above the radiator. These, and the looms to them from the dizzy etc, can go bad, replacing them (unless someone here can tell you how to test them) is a god plan. The looms you will have to build yourself as I believe they are NLA.
The B bank (LHS) fuel pressure regulator may be duff, worth changing it anyway, and the RHS one, if fitted, can be bypassed as it does nothing useful.
FWIW, the crank position sensors front and rear would be the first thing I would change, and the gap between the rear sensor and the ring gear is critical. If you ask Warrjon, he will tell you the gap spec. As already mentioned, of you have not replaced the fuel filter and cleaned out the sump tank under the battery, that is the first thing, IMO, followed by a spark timing check on A1 and B1 cylinder
Last edited by Greg in France; 12-29-2018 at 03:49 AM.
Just to clarify,car is a 1988 and has the Marelli ignition system. I have focused my fault diagnosis on to things i have changed or fiddled with as I drove it into the garage.
Couple of questions again...
has anyone else ran Denso plugs and they have been fine?
Where is the fuel filter located,presumably under the back of the car by the pump?
There is a smell of fuel around the back of the car, I have read this is normal.....doesn't seem normal to me, can anyone confirm or deny this?
Appreciate fuel pressure at the fuel rail is ok but also know this does not necessarily represent flow rate,if I put a pie from the fuel rail entry into a bottle what l/h can I expect from a good pump?
No water anywhere near the engine
I have not checked the resistor pack, the bonnet of off the car so I locating it should be easy bit how to I then check its function?
Orangeblossom - I have made myself a coffee and shall read your thread!
Thanks again
Simon
Must be a 1989 for Marelli, unless your market got cursed with it earlier than the rest of us.
1) NGK only down here, gapped to 0.025".
2) Behind the spare wheel in the boot.
3) Lack of fire up front = petrol smell down the rear, "normally".
4) I'd have to go searching, but a 2ltr container filled in a few seconds is a good start.
5) OK for now. Mine get a bath every year or so.
6) You DONT. Remove the plug, FUN, clean the plug and the apposing section of the "pack", and then do it again. I use Lemon juice, the REAL stuff, NOT the bottled crap.
7) Cup of Tea, oh boy, that car has NO hope, HAHA, BEER mate, gotta have BEER. Everything becomes as clear as mud after 4 or 5.
The ONLY Marelli car I have ever seen and got running for the guy, had a scungy connection for the FRONT sensor, just down below the oil filler cap area. Seperated, cleaned with the "juice", replugged, fire in the belly, 2 beer repair, simple.
Last edited by Grant Francis; 12-29-2018 at 03:31 AM.
The Fuel Pump and The Fuel Filter are underneath the Battery in the Boot/Trunk a little bit of a PIA to get to, which is why I didn't put it back in exactly the same position that I found it!
New Fuel Filter about £10 (uk) New Fuel Pump about £35 (uk) on ebay (with a 2 year guarantee!) no need to Spend £200 as they are Generic and fitted to lots of different Cars
The Fuel Pump is Fed by Gravity, so don't go pulling hoses off until you've drained the Tank or you will have more Petrol Flooding everywhere than you know what to do with
In order to drain the Fuel Tank, there is a rubber Blanking Grommet underneath the Car, just opposite the Rear 'Muffler/Exhaust'
Underneath that 'Blanking Grommet' is a Tap that needs a Socket to undo it, then put a plastic tube over the Spout and then drain the whole lot out
Also underneath the Battery is the Sump Tank, which is what you are draining when you undo that Tap
Fuel Tank>Sump Tank>Fuel Pump>Fuel Filter
The Sump Tank can get full of 'Crud' so after draining the Petrol Out, Knock round the Locking Ring on the Sump Tank with a Piece of Wood to avoid any Sparks!
Inside the Sump Tank underneath that Locking Cap, is another Filter which you could either Clean out or replace
Nothing complicated really, replacing the Fuel Pump and Filter can be done in a Couple of hours
Fuel Pump/Filter and Sump Tank XJS V12 Marelli Car all very easy to replace
'The Sump Tank' after draining the Fuel Tank, knock that locking ring round with a piece of wood to undo it and underneath that locking ring is a Filter
Location of the Drain Tap for the Sump Tank underneath a Rubber Blanking Grommet
Drain Tap for the Sump Tank
As for the Spark Plugs I was warned off using the Iridium ones and so I use these instead
Never had a problem using these and always starts first time
Replaced filter, I blew through the old one and there was a lot of restriction, new one much better.
Drained surge tank and checked for debris. Got a load of petrol in the face so I guess I am now part of the club. All very clean, the petrol,not the face.
Pulled off front 2 injectors, disconnected coils, turned over. Both injectors fired well into a clear bottle.
Cleaned the connectors of the resistor pack with contact cleaner and a small wire brush.
Pulled off fuel lines from FPR and I have read that if they are ok they don't leak and diaphragm inside is still intact?
Put it all back together and still didn't run, chugged and died exactly as before.
I think I have eliminated fuelling as an issue, the injectors seem to fire well on both bank A & B. Although I checked for a spark from every plug lead I am not convinced its a strong one. I am going for a new crank sensor and dizzy cap I think....???
Also anyone know what the pipe is supposed to be attached to? Its on the rear RHS of the motor and can't find a home for this end.....
Pulled off fuel lines from FPR and I have read that if they are ok they don't leak and diaphragm inside is still intact?
Well, yes and no.
No leaks and an intact diaphragm are good things, obviously....but neither ensures that pressure is being correctly regulated. Only testing with a pressure gauge will verify that.
I think I have eliminated fuelling as an issue, the injectors seem to fire well on both bank A & B. Although I checked for a spark from every plug lead I am not convinced its a strong one. I am going for a new crank sensor and dizzy cap I think....???
A strong blue/white spark is important, yes. An orange-ish spark is weak.
I'm not sure if a dodgy crank sensor would change the quality of the spark.
However, I think a sensor problem (fairly common) might cause a hard starting problem by way of a degraded "TDC" signal to the ignition ECU. Let's hear what others have to say about that.
Somewhere in the archives you'll find resistance specs for the sensor. And, sometimes, the air gap becomes clogged with debris, degrading the function.
Also anyone know what the pipe is supposed to be attached to? Its on the rear RHS of the motor and can't find a home for this end.....
Looks like you have RHD car. UK specification? Australian? Different markets had different gizmos and vacuum hoses. Knowing the market spec might help narrow things down
Yes its RHD UK car. I must have 25 pictures of XJS engine bays saved and every one is different!
I had a dodgy connector on the crank sensor before and it didn't fire at all, cleaned this and it fired right up.....these things usually work or don't I guess....
Your lack of a Strong Spark is much more likely to be down to the Ignition Amplifiers on the Closing Panel, that goes over the Top of the Rad
Unplug these and clean their plugs and sockets, then put the plugs back and see if that makes any difference
I really hope that its only a case of dirty/corroded Plugs as those Ignition Amplifiers are
(and you better sit down for this) £200 a piece!
And they need to be remounted with Thermal Paste, the same as you use to heat sink a CPU in a Computer
In any event in the Scheme of things, it wouldn't do any harm to replace the FPR on 'B' Bank, as the rubber diaphragms inside do not last for ever and are only about £45
Ignition Amplifiers on the Top Closing Panel of a Marelli XJS V12 Try Cleaning the Plugs and Sockets, as they are very expensive!
If you need to fit New Ignition Amplifiers, they need to be remounted with Thermal Paste like you would use for a Computer CPU
Already had the ignition amps off and cleaned them, not reapplied the paste yet though..... Tbh it never crossed my mind it could be them but your right it could be.
I guess there is a way to check there functionality???
That Vacuum Pipe you are holding in the Photo needs to be put back and not left hanging, as any sort of Vacuum leak will almost certainly have an effect on the way that She is running
If you removed the Ignition Amplifiers for Cleaning, I would go and remount them with 'Thermal Paste' before you do anything else, because they need to have 'Thermal Contact' with those 2 Aluminum Blocks of metal that they are sitting on
Or else you could fry all £400 quids worth!
You don't need a giant sized tube like I've got in that photo, any Computer Shop should sell that Stuff or get some off ebay
12-28-2018, 01:27 PM
XJS V12 starting trouble....
